DON’T PANIC! BIG ROCK WILL NOT HIT US TODAY

OK, everyone take a deep breath. An asteroid half the length of a football field will fly close to Earth today. Despite what you might have read on some sketchy websites, there’s zero chance that it will hit the planet, even though it’ll zip inside the orbit of weather satellites.

This isn’t some Bruce Willis-Ben Affleck “Armageddon” moment when the fate of Earth is in doubt. The 286-million-pound rock, formally known as 2012 DA14, is expected to scoot over the Indian Ocean late Friday morning. Most people won’t even see it.

Think of this as a teachable moment. NASA does.

“This is a reminder that there are asteroids out there and that they pose a hazard and that not all of them have been discovered yet, particularly ones of this size,” said Paul Chodas, a researcher at NASA’s Near-Earth Object Program in Pasadena.

NASA estimates there are about 500,000 near-Earth asteroids like 2012 DA14, and that only 1 percent have been found. An asteroid the size of 2012 DA14 buzzes Earth about once every 40 years, according to the agency. And the planet is hit by an object like this once every 1,200 years.

Asteroid 2012 DA14, which was spotted last year by amateur astronomers, is getting a lot of attention because it is the largest object of its kind ever forecast to come this close to Earth.

Comparatively little is known about 2012 DA14. It’s hard to see. NASA won’t be able to fully determine its size, composition and spin until the asteroid gets within range of powerful radar systems.

But scientists are certain that an object like 2012 DA14 could cause tremendous damage if it struck Earth. The outcome would be similar to the Tunguska event, an explosion that occurred in Earth’s atmosphere in June 1908, when a meteoroid or comet reached the planet over Russia. The air burst wiped out upward of 80 million trees over a 830-square-mile area.

Chodas said that if 2012 DA14 hit San Diego — which, to repeat, isn’t going to happen — the asteroid would deliver about 200 times the energy of the atomic bomb that was dropped on Hiroshima, Japan, in August 1945. That bomb killed about 150,000 people.

The asteroid’s energy would damage or destroy an area 10 to 15 miles in radius and would probably create an air blast knocking people off their feet 30 miles from the center of the blast. Ejected matter from the asteroid could be visible from as far away as Los Angeles. If the asteroid landed just offshore, it could cause a tsunami.

How might the public react to news of an impending collision?

“It would depend on how much lead time your warning gave people,” said Kim Stanley Robinson, a University of California San Diego graduate who became a best-selling science fiction author. “Generally, this kind of prediction is made a few years in advance. Also, it’s not a completely deterministic thing, with certainty as to impact zone. So they couldn’t say ‘San Diego.’ So in essence, your scenario isn’t the way things would really work, which makes it bad or weak science fiction from the start.”

Robinson added: “There are proposed methods for changing asteroids in their routes enough so that they would miss Earth, which sometimes come down to painting one side of the asteroid white or running a robot spaceship next to it for a couple of years. Presumably if a big rock were clearly headed toward Earth, we would try some of these methods. It may also be true that some nuclear blasts that were far enough away to keep from breaking the asteroid up but close enough to alter its orbit might be in the cards.